Too much light may spur cancer

A researcher says it can suppress a hormone, throwing off women's bodies.

October 19, 2006|By Susan Brink Los Angeles Times

Some cancers might be rooted to too many hours exposed to artificial light, according to Richard G. Stevens, cancer researcher at the University of Connecticut Health Center.

His work is based on the theory that the increase in breast cancer in the industrialized world is linked to the disruption of hormone cycles.

Light, he says, suppresses production of the hormone melatonin, which allows levels of estrogen to rise. And when lights are on long after dark, it confuses women's circadian clocks, the roughly 24-hour internal rhythm that keeps hormones and organs on their daily schedule.

"Cells don't know when not to divide," he said.

His theory was bolstered by a 1991 Centers for Disease Control and Prevention report showing that blind women are about half as likely as sighted women to get breast cancer.

An October 2005 study looked at sleep patterns of more than 12,000 women. Although researchers found no statistically significant increase in cancer risk among short sleepers, said Stevens, an author of the study, the risk estimates were consistently lower in long sleepers.

"We don't know why breast cancer is increasing in industrialized societies," he says. Until more is known, he advises women to get adequate sleep -- and to do it in a very dark room.